A molecular dynamics simulation study of relaxation processes in the dynamical fast component of miscible polymer blends

Molecular dynamics simulations of model miscible polymer blends consisting of 1,4-polybutadiene (PBD) (slow component) and PBD chains with reduced or eliminated dihedral barriers (fast component) have been performed in order to study the influence of blending on segmental relaxation processes in the fast component. We find that blending with a slow (high glass transition temperature, or T-g) component significantly increases the separation between the alpha- and beta-relaxations of the fast (low T-g) component, which may be unresolvable or nearly unresolvable in the pure melt. The alpha-relaxation of the fast component is strongly influenced by blending, moving to longer relaxation times with increasing concentration of the slow component. In contrast, the relaxation time of the beta-process of the fast component is only weakly influenced by blending. We speculate that this separation of relaxations processes in the fast component with blending can explain segmental relaxation behavior observed in dielectric and NMR relaxation studies of miscible polymer blends with disparate component dynamics.